Rectangular cathodic arc source and method of steering an arc spot

ABSTRACT

The invention provides an arc coating apparatus having a steering magnetic field source comprising steering conductors disposed along the short sides of a rectangular target behind the target, and a magnetic focusing system disposed along the long sides of the target in front of the target which confines the flow of plasma between magnetic fields generated on opposite long sides of the target. The plasma focusing system can be used to deflect the plasma flow off of the working axis of the cathode. Each steering conductor can be controlled independently. In a further embodiment, electrically independent steering conductors are disposed along opposite long sides of the cathode plate, and by selectively varying a current through one conductor, the path of the arc spot shifts to widen an erosion corridor. The invention also provides a plurality of internal anodes, and optionally a surrounding anode for deflecting the plasma flow and preserving a high ionization level of the plasma. The invention also provides a shield at floating potential, restricting the cathode spot from migrating into selected regions of the target evaporation surface outside of the desired erosion zone. The shield may be positioned immediately above the region of the target surface in the vicinity of the anode, protecting the anode from deposition of cathodic evaporate and providing better distribution of cathodic evaporate over the substrates to be coated. The invention further provides correcting magnets adjacent to the short sides of the target, to move the arc spot between the long sides.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit under all relevantU.S. statutes, including 35 U.S.C. 120, to U.S. application Ser. No.09/958,703 filed Jan. 3, 2002, titled RECTANGULAR CATHODIC ARC SOURCEAND METHOD OF STEERING AN ARC SPOT in the name of Vladimir Gorokhovsky,which claims the benefit under 35 U.S.C. 365 to PCT Appl. No.PCT/CA00/00380 filed Apr. 7, 2000, which in turn claims priority toCanadian Appl. No. 2,268,659 filed Apr. 12, 1999.

FIELD OF INVENTION

[0002] This invention relates to apparatus for the production ofcoatings in a vacuum. In particular, this invention relates to a vacuumarc coating apparatus having a rectangular cathodic arc source providingimproved arc spot scanning and a plasma focusing system.

BACKGROUND OF THE INVENTION

[0003] Many types of vacuum arc coating apparatus utilize a cathodic arcsource in which an electric arc is formed between an anode and a cathodeplate in a vacuum chamber. The arc generates a cathode spot on a targetsurface of the cathode, which evaporates the cathode material into thechamber. The cathodic evaporate disperses as a plasma within thechamber, and upon contact with one or more substrates coats thesubstrates with the cathode material, which may be metal, ceramic etc.An example of such an arc coating apparatus is described in U.S. Pat.No. 3,793,179 issued Feb. 19, 1974 to Sablev, which is incorporatedherein by reference.

[0004] An arc coating apparatus of this type is advantageous for use inthe coating of large substrates and multiple substrates, due to thelarge surface area of the cathode which can be evaporated into a largevolume coating chamber. However, in a large surface area cathode arccoating apparatus of this type a significant portion of the targetevaporation surface of the cathode plate goes largely unused, due to thescanning pattern of arc spots which follows certain physical principles:

[0005] 1. The arc discharge tends to move in a direction which reducesthe voltage drop in the arc circuit, and the arc spot thus tends tomigrate to regions on the target surface which are closest to the anodiccurrent conductor. Where multiple current conductors traverse thecathode the arc spot will occasionally migrate into the region betweenconductors where it may remain for a considerable time because nosteering mechanism is present to move the arc spot back to the desiredevaporation zone.

[0006] 2. In the case of metal cathodes the arc spot follows aretrograde motion according to the “anti-ampere force” principle, and isthus attracted to the coaxial magnetic force lines generated by theanodic current conductor.

[0007] 3. In the case of a cathode formed from a material which does nothave a melting phase, for example a sintered or graphite cathode, thearc spot moves according to the “ampere force” principle and is repelledfrom the coaxial magnetic force lines generated by the anodic currentconductor.

[0008] 4. The arc spot is attracted to the region where the tangentialcomponent of a transverse magnetic field is strongest.

[0009] 5. The arc spot tends to migrate away from the apex of an acuteangle at the point of intersection between a magnetic field line and thecathode target surface (the “acute angle” rule).

[0010] These effects result in a limited erosion zone relative to theavailable area of the target surface of the cathode plate, reducing thelife of the cathode and dispersing cathodic evaporate into the coatingchamber in non-uniform concentrations.

[0011] In a large area cathode arc coating apparatus using a metalcathode plate the anti-ampere motion of the arc spot and the tendency ofthe arc to seek the lowest voltage drop combine to largely confine thearc spot to the vicinity of the anodic conductor, substantially limitingthe erosion zone to the region of the target surface surrounding theanodic conductor. This results in a very small area inside the coatingchamber in which the cathodic evaporate is concentrated enough to applya uniform coating to the substrates. However, it is not possible toconstruct the cathode plate so that the desired coating material islocated only in the erosion zone, since the arc spot will occasionallystray out of the erosion zone and if the target surface is not entirelycomposed of the selected coating material the cathodic evaporate fromoutside the desired erosion zone will contaminate the coating on thesubstrates.

[0012] In the case of a cathode plate formed from a material which doesnot have a melting phase, the tendency of the arc spot to move in anampere direction, away from the region of the anodic conductor, isopposed by the tendency of the arc discharge to settle toward the regionof lowest voltage drop. In these cases the arc spot tends to movechaotically over the target surface of the cathode and the cathodicevaporate accordingly disperses in random locations and non-uniformconcentrations within the coating chamber, rendering uniform coating ofthe substrates improbable. This random motion also causes the arc spotto move off of the target surface of the cathode and causes undesirableerosion of non-target portions of the cathode plate, for example theside edges.

[0013] U.S. Pat. No. 4,448,659 issued May 15, 1984 to Morrison, which isincorporated herein by reference, describes an arc coating apparatusproviding a cathode in the form of a plate with a large target surfacefor creating cathodic evaporate. A confinement ring composed of amagnetically permeable material surrounds the cathode to confine the arcspot to the target surface. Such plasma sources can be used for theproduction of coatings on large and long articles, but present thefollowing disadvantages:

[0014] 1. Despite the initial low probability of the presence ofcathodic spots on the protective ring, over time the cathodic evaporatecoats the ring and cathodic spots are produced on the ring withincreasing frequency. This results in contamination of the coating bythe ring material, and ultimately in ring failure.

[0015] 2. In self-steering cathodic arc sources it is not possible touse external magnetic fields in the vicinity of the target surface ofthe cathode. It is therefore not possible in such an apparatus to use aplasma-focusing magnetic field, as the influence of the focusingmagnetic field makes the distribution of cathodic spots on the workingsurface of the cathode irregular and non-uniform. Any external magneticfield, for example for focusing or deflecting the arc plasma flow,interferes with the self-sustained magnetic field generated by thecathode and anode current conductors and disrupts the self-steeringcharacter of the cathode spot. However, the absence of magnetic focusingreduces the efficiency of the coating process and impairs the quality ofsubstrate coatings, because the content of the neutral component(macroparticles, clusters and neutral atoms) in the region of thesubstrates, and thus in the substrate coating, increases.

[0016] 3. A cathode in this type of plasma source rapidly becomesconcave due to evaporative decomposition, and its useful life istherefore relatively short. Moreover, since the evaporation surface ofthe cathode becomes concave in a relatively short time it is practicallyimpossible to use a high voltage pulse spark igniter in such a design,so that a mechanical igniter must be used which lowers workingreliability and stability.

[0017] 4. While the confinement ring prevents the arc spot from strayingoff of the target surface, it does not affect the tendency of the arcspot to migrate toward the anodic conductor in the case of metalcathodes, or to move chaotically over the target surface in the case ofnon-metal cathodes.

[0018] Accordingly, self-steering arc plasma sources tend to use thetarget surface inefficiently and the cathode thus has a relatively shortuseful life.

[0019] The erosion efficiency of the target surface can be improved byproviding an arc spot steering system to steer the arc spot along aselected path about the target surface. This increases the size of theregion within the coating chamber in which coating can occur.

[0020] For example, the scanning pattern of a cathode spot can becontrolled by providing a closed-loop magnetic field source disposedbeneath the target surface of the cathode, in a manner similar to thatdescribed in U.S. Pat. No. 4,724,058 issued Feb. 9, 1988 to Morrison,which is incorporated herein by reference. The magnetic field sourceestablishes a magnetic field in a selected direction over the targetsurface, which directs the cathode spot in a direction substantiallyperpendicular to the direction of the magnetic field and thus providesmore efficient evaporation of the target surface. This approach is basedon the principle of arc spot motion whereby an arc spot is attracted tothe region where the tangential component of a transverse magnetic fieldis strongest.

[0021] However, this still significantly limits the area of the targetsurface of the cathode which is available for erosion, because this typeof arc coating apparatus creates a stagnation zone in the region wherethe tangential component of the magnetic field is strongest. The cathodespot eventually settles in the stagnation zone, tracing a retrogradepath about the erosion zone and creating a narrow erosion corridor onthe target surface. This limits the uniformity of the coating on thesubstrates and reduces the working life of the cathode.

[0022] U.S. Pat. No. 5,997,705 issued Dec. 7, 1999 to Welty, which isincorporated herein by reference, teaches a rectangular cathode plate inwhich the evaporation surface is located on the peripheral edge of thecathode plate, the arc spot being confined to the evaporation surface bycathode shields disposed over opposed faces of the cathode plate.Deflecting electrodes disposed about the cathode plate direct the plasmastream in two directions, parallel to the faces of the cathode plate.

[0023] In this apparatus the substrates must surround the edges of thecathode plate, and the cathode plate occupies most of the space withinthe apparatus. Thus, in order to coat a significant number of substratesthe cathode plate, and thus the apparatus itself, must be extremelylarge. Also, filtration in this apparatus is poor, since the substratesare directly exposed to droplets and macroparticles entrained in thecathodic evaporate.

[0024] A deflecting electrode is described in U.S. Pat. No. 5,840,163issued Nov. 24, 1998 to Welty, which is incorporated herein byreference. This patent teaches a rectangular vacuum arc plasma source inwhich a deflecting electrode is mounted inside the plasma duct andeither electrically floating or biased positively with respect to theanode. However, this device requires a sensor which switches thepolarity of the magnetic field when the arc spot on the rectangularsource has reached the end of the cathode, in order to move the arc spotto the other side of the cathode. This results in an undesirable periodwhere the magnetic field is zero; the arc is therefore not continuous,and is not controlled during this period. Consequently this‘psuedo-random’ steering method cannot consistently produce reliable orreproducible coatings.

[0025] U.S. Pat. No. 4,673,477 to Ramalingam proposes that the magneticfield source can be moved to shift the magnetic field lines and increasethe utilization efficiency of the target surface. However, themechanical adaptations required for such a system make the apparatus toocomplicated and expensive to be practical.

[0026] Where an external magnetic field is present the arc spot followsthe “acute angle” rule, according to which the arc spot tends to migrateaway from the apex of an acute angle at the point of intersectionbetween a magnetic field line and the cathode target surface. The basicprinciple is that a cathodic spot formed by a vacuum arc in a fairlystrong magnetic field (in the order of 100 Gauss), the force lines ofwhich cross the surface of the cathode at an acute angle, will move in areverse (retrograde) direction perpendicular to the tangential componentof the field and, concurrently, displace away from the apex of the angle(for example, see Cathodic Processes of Electric Arc by Kesaev I. G.,Nauka, 1968). This results in the arc spot settling beneath the apex ofthe arch-shaped portion of the magnetic field which projects over thetarget surface.

[0027] U.S. Pat. No. 5,587,207 issued Dec. 24, 1996 to Gorokhovsky,which is incorporated herein by reference, teaches that cathode spotconfinement under a closed loop-type linear anode can be enhanced by aconductor which encases the anode to form a closed loop magnetic coil,with the magnetic field lines oriented in the direction shown in FIGS.29 and 30 therein. Simultaneous use of both the closed-loop magneticsteering coil behind the cathode and a closed-loop linear anode in frontof the target evaporation surface (with or without an enclosed magneticcoil) results in a synergistic improvement of arc discharge stabilityand thus cathode spot motion. The anode can be configured in any desiredpattern, the configuration thereof being limited only by the peripheryof the target surface. The arc spot will scan the target surface underthe influence of the transverse magnetic field (in an ampere directionin the case of cathodes of carbon and related sintered materials or inan anti-ampere direction in the case of metal cathodes), virtuallyunaffected by the current flowing through the anodic conductor.

[0028] A disadvantage of this approach is that the arc spot willoccasionally migrate from the selected erosion zone to another part ofthe cathode target surface where the intensity of the transversemagnetic field is small and, there being no means available to returnthe arc spot to the desired erosion zone, will stagnate in the lowmagnetic field region. In the case of a carbon-based cathode plate, whenthe velocity of arc spot movement is low enough the arc spot can settlein any stagnation zone where the transverse magnetic field is close tozero, and will not return to the erosion zone.

[0029] U.S. Pat. No. 5,435,900 issued Jul. 25, 1995 to Gorokhovsky,which is incorporated herein by reference, discloses a deflectingmagnetic system surrounding a parallelipedal plasma guide, in which thedeflecting conductors force the plasma toward the substrate holder.However, this patent does not address the problem of magneticallysteering an arc spot around a rectangular cathode plate in the presenceof a deflecting magnetic field.

SUMMARY OF THE INVENTION

[0030] The present invention overcomes these disadvantages by providinga steering magnetic field source comprising a plurality of electricallyindependent closed-loop steering conductors disposed in the vicinity ofthe target surface. In the preferred embodiment each steering conductorcan be controlled independently of the other steering conductors.

[0031] The steering conductors may be disposed in front of or behind thetarget surface of the cathode plate. When disposed in front of thetarget surface the steering magnetic field lines intersect with thetarget surface at an obtuse angle, which obviates the motion-limitingeffect of the acute angle principle and allows the arc spot to move overa larger region of the target surface, thereby further increasing thesize of the erosion zone.

[0032] Steering conductors disposed in front of the target surface canalso serve as focusing conductors, which confine the plasma and directit toward the substrates. In these embodiments opposed steering/focusingconductors disposed along the long sides of the cathode plate generatemagnetic cusps which create a magnetic pathway within which the plasmaflows toward the substrates. Additional focusing conductors may bedisposed along the plasma duct downstream, preferably with magneticfields that overlap within the plasma duct to create a continuousmagnetic wall along the plasma duct.

[0033] Increasing the current through one steering conductor increasesthe strength of the magnetic field generated by that conductor relativeto the strength of the magnetic field of the steering conductor alongthe opposite side of the cathode plate, shifting the magnetic field onthe opposite side of the cathode plate transversely. Selectiveunbalancing of the steering conductor currents can thus compensate forthe magnetic influence of the focusing conductors, and if desired canincrease the effective breadth of the erosion zone to thus provide moreuniform erosion of the target surface and a larger area within thecoating chamber in which the cathodic evaporate is dispersed atconcentrations sufficient to uniformly coat the substrates.

[0034] In a further embodiment, groups of steering conductors aredisposed along opposite sides of the cathode plate. By selectivelyapplying a current through one conductor in each group, the path of thearc spot shifts to an erosion corridor defined by the active steeringconductor.

[0035] The present invention further provides means for restricting thecathode spot from migrating into selected regions of the targetevaporation surface outside of the desired erosion zone. The inventionaccomplishes this by providing a shield at floating potential positionedover one or more the selected regions of the target evaporation surface,which prevents the arc spot from forming in or moving into the shieldedregion. In one preferred embodiment the shield is positioned immediatelyabove the region of the target surface in the vicinity of the anode,spaced from the target surface. The evaporation zone is thus restrictedto the area of the target surface surrounding the shield, protecting theanode from deposition of cathodic evaporate and providing betterdistribution of cathodic evaporate over the substrates to be coated,which results in more uniform coatings over a greater coating area.

[0036] The shield can be used to keep arc spots away from any regionwhere the negative conductor traverses the cathode, which represents thelowest voltage drop relative to the anode. Where a large anode ormultiple anodes are provided the shield restrains the arc spot frommigrating into the region of the cathode located beneath an anode, wheremost of evaporated material would be trapped by the anode rather thanflowing to the substrate.

[0037] Further, the presence of the shield allows the target evaporationsurface of the cathode plate to be constructed of a combination of thecoating material and another material, for example an expensive coatingmaterial such as titanium or platinum in the desired erosion zone and aninexpensive material such as steel outside of the erosion zone. Thesteel portion of the target surface may be shielded by a floating shieldof the invention to prevent cathode spot formation and motion thereon,and thus prevent contamination of the coating while optimizingutilization of the expensive coating material.

[0038] In an arc coating apparatus utilizing a magnetic steering system,regions where the transverse magnetic field is low can be shielded inthe same manner to exclude movement of the arc spot into these regionsand create the desired pattern of erosion. In this embodiment of theinvention the target may be placed on the poles of magnetron-typemagnetic system of the type described in U.S. Pat. No. 4,724,058 issuedFeb. 9, 1988 to Morrison, which is incorporated herein by reference. Theregion of the evaporation surface located about the central part oftarget cathode, where the tangential component of the magnetic field istoo weak to confine arc spots, may be shielded by a floating shieldwhich prevents the arc spot from migrating into the stagnation areacreated between the magnetic fields generated by the magnetron.

[0039] The invention further provides a magnetic focusing system whichconfines the flow of plasma between magnetic fields generated onopposite sides of the coating chamber. This prevents the plasma fromcontacting the surface of the housing, to avoid premature deposition,and increases the concentration of plasma in the vicinity of thesubstrate holder.

[0040] In a further embodiment the plasma focusing system can be used todeflect the plasma flow off of the working axis of the cathode, toremove the neutral component of the plasma which otherwise constitutes acontaminant. In this embodiment the plasma focusing coils are disposedin progressively asymmetric relation to the working axis of the cathode,to deflect the flow of plasma along a curvate path toward a substrateholder.

[0041] The present invention thus provides a vacuum arc coatingapparatus comprising a rectangular cathode plate having opposed longsides and opposed short sides and connected to a negative pole of an arccurrent source, the cathode plate having an evaporation surface, acoating chamber defined by the evaporation surface and a housing,containing a substrate holder, at least one anode within the coatingchamber spaced from the evaporation surface, connected to a positivepole of a current source, an arc igniter for igniting an arc between thecathode and the anode and generating an arc spot on the targetevaporation surface, a magnetic steering system comprising at leastfirst and second steering conductors respectively arranged behind theevaporation surface along the short sides of the cathode plate, thefirst steering conductor carrying a current in a direction opposite to adirection of current in the second steering conductor, the first andsecond steering conductors being disposed in the vicinity of theevaporation surface so that a magnetic field generated thereby exerts amagnetic influence on the arc spot, and a magnetic focusing systemcomprising at least first and second substantially linear focusingconductors arranged in front of the evaporation surface along oppositelong sides of the cathode plate, the focusing conductors carrying acurrent in opposite directions and being electrically independent of thesteering conductors, wherein the magnetic fields generated by thesteering conductors and the magnetic fields generated by the focusingconductors are oriented in the same direction in front of theevaporation surface to thereby direct plasma away from the evaporationsurface and direct arc spots in a desired direction around theevaporation surface.

[0042] The present invention further provides a method of steering anarc spot around a rectangular cathode plate having long sides and shortsides and a front evaporation surface, comprising the steps of a.generating a magnetic field in front of the evaporation surface in afirst direction along a first long side of the cathode plate andgenerating a magnetic field in front of the evaporation surface in asecond direction opposite the first direction along a second long sideof the cathode plate, and b. generating a magnetic field behind theevaporation surface in a third direction along a first short side of thecathode plate and generating a magnetic field behind the evaporationsurface in a fourth direction opposite the third direction along asecond short side of the cathode plate, wherein the magnetic fieldsextend in front of the evaporation surface to steer the arc spot alongan erosion zone around the evaporation surface.

[0043] The present invention further provides a method of steering anarc spot around a rectangular cathode plate having long sides and shortsides and a front evaporation surface, the cathode plate being containedwithin an apparatus having a plurality of electrically isolated anodeblocks spaced from the cathode plate in front of the evaporationsurface, comprising the step of selectively activating and deactivatinganode blocks to move the arc spot around the evaporation surface.

[0044] Further aspects and embodiments of the invention and of apparatusfor implementing the methods of the invention will be apparent from thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In drawings which illustrate by way of example only a preferredembodiment of the invention,

[0046]FIG. 1 is a schematic cross-section of a prior art large areacathode vacuum arc plasma source having a magnetic steering systemdisposed behind the cathode plate;

[0047]FIG. 2 is a partial perspective view illustrating the distributionof magnetic field lines produced by a magnetic steering system accordingto one embodiment of the invention;

[0048]FIG. 2a is a schematic elevation illustrating balanced magneticfield lines produced by the magnetic steering system of FIG. 2;

[0049]FIG. 2b is a schematic elevation illustrating an erosion corridorproduced by the magnetic steering system of FIG. 2 unbalanced in a firstdirection;

[0050]FIG. 2c is a schematic elevation illustrating an erosion corridorproduced by the magnetic steering system of FIG. 2 unbalanced in asecond direction;

[0051]FIG. 3 is a schematic elevation illustrating a variation of theembodiment of FIG. 2 in which multiple steering conductors are disposedalong the long sides of the cathode plate;

[0052]FIG. 4 is a plan view of a further preferred embodiment of a largearea cathode arc source of the invention;

[0053]FIG. 5 is a cross-section of the apparatus of FIG. 4 taken alongthe line 5-5;

[0054]FIG. 6a is a cross-section of the apparatus of FIG. 4 taken alongthe line 6-6;

[0055]FIG. 6b is a cross-sectional elevation of a further embodiment ofthe apparatus of FIG. 4 having multiple pairs of steering conductors;

[0056]FIG. 7a is a plan view of an arc coating apparatus embodying aplasma focusing system according to the invention having a plurality oflinear anodes and a single cathode target;

[0057]FIG. 7b is a side elevation of the arc coating apparatus of FIG.7a;

[0058]FIG. 7c is a side elevation of the arc coating apparatus of FIG.7a with plurality of cathode targets installed in the same housing;

[0059]FIG. 7d is a plan view of an arc coating apparatus of FIG. 7c;

[0060]FIG. 8 is a plan view of a variation of the arc coating apparatusof FIG. 7a providing neutralizing conductors for modulating the steeringand focusing conductors;

[0061]FIG. 9 is a plan view of an arc coating apparatus embodying adeflecting electromagnetic system according to the invention for guidingcathodic evaporate to a substrate holder disposed remote from theworking axis of the cathode plate;

[0062]FIG. 10 is a plan view of a dual arc coating apparatus embodyingthe magnetic steering, focusing and deflecting aspects of the invention;

[0063]FIG. 11 is a cross-sectional side elevation of a furtherembodiment of the arc coating apparatus according to the invention;

[0064]FIG. 12 is a cutaway front elevation of the arc coating apparatusof FIG. 11; and

[0065]FIG. 13 is a rear elevation of the arc coating apparatus of FIG.11.

DETAILED DESCRIPTION OF THE INVENTION

[0066]FIG. 1 illustrates a prior art large area rectangular cathodevacuum arc plasma source of the type described and illustrated in U.S.Pat. No. 4,724,058 to Morrison, which is incorporated herein byreference. The apparatus 10 comprises a cathode plate 12 having a targetevaporation surface 14 which may be circumscribed by a confinementmember 16 composed of a magnetically permeable material. As described inU.S. Pat. No. 5,587,207 issued Dec. 24, 1996 to Gorokhovsky, which isincorporated herein by reference, an anode 15 disposed opposite thetarget surface 14, which may be composed of a metallic or a non-metalliccoating material.

[0067] A current applied between the cathode 12 and the anode 15 createsan arc which generates an arc spot on the target surface 14. In theprior art apparatus shown the scanning pattern of the cathode spot iscontrolled by a closed-loop magnetic field source 18 disposed behind thecathode 12. The magnetic field source 18 establishes magnetic fields 19a, 19 b in a opposite directions over the target surface 14 which movesthe arc spot in a retrograde motion according to the formula

V _(cs) =−c[I _(as)(B _(t))]

[0068] in which Vcs is the velocity of the arc spot, Ias is the arc spotcurrent, Bt is the strength of the transverse magnetic field, and c is acoefficient based on the material of the target surface 14. The arc spotthus traces a retrograde path about the cathode plate following thelength of the magnetic field source.

[0069] When trapped within the static magnetic field produced by themagnetic field source 18, the cathode spot is directed toward the apexof the magnetic field lines 20, the region where the tangentialcomponent of a magnetic field is strongest, which causes the targetsurface 14 to evaporate along a narrow evaporation corridor 14 a.Further, the oppositely oriented magnetic field lines 19 a, 19 b createa stagnation zone at 22 in which the cathode spot can settle and remainfor prolonged periods, eroding the target surface 14 unduly in thestagnation zone 22. Both of these effects result in poor utilizationefficiency of the target surface 14. Accordingly, in the apparatusdescribed in U.S. Pat. No. 4,724,058 the magnetic field is activatedonly intermittently during the coating process, the arc spot being freeto scan randomly most of the time. Since the cathode spot is largelyself-steering, magnetic fields cannot be used for plasma focusing.

[0070]FIG. 2 illustrates a preferred embodiment of a cathode spotsteering system 60 according to the invention. In the embodimentillustrated in FIG. 2 the steering system 60 is disposed behind thecathode plate 32 (i.e. on the side of the cathode plate 32 opposite tothe target evaporation surface 34), which has long sides 32 a, 32 b andshort sides 32 c, 32 d. The steering system 60 comprises linearconductors 62 and 64 respectively disposed in parallel with the longsides 32 a, 32 b of the cathode plate 32 having a current I_(LS) appliedthereto in the direction shown, and linear conductors 66 and 68respectively disposed in parallel with the short sides 32 c, 32 d of thecathode plate 32 having a current I_(SS) applied thereto in thedirection shown. The conductors 62, 64 are disposed behind the cathodeplate in the vicinity of the target surface 34 so that the magneticfields generated thereby intersect the target surface 34, and thusinfluence arc spot formation and motion. The steering conductors 62, 64,66, 68 may alternatively be disposed in front of the cathode plate, asin the embodiment illustrated in FIGS. 4 to 6, described below. Ineither case the steering magnetic field source 60 generates a magneticfield defining an erosion zone 70 along the target surface 34.

[0071] The configuration and polarities of the magnetic fields generatedby the steering conductors 62, 64, 66 and 68 are illustrated by themagnetic field lines in FIG. 2. The magnetic field lines projectingabove the target surface 34 are arch-shaped, and on opposite sides ofthe cathode 32 are oriented in opposite directions. Arc spots movingwithin the erosion zone 70 are attracted toward the apex of thearch-shaped magnetic field lines, where the tangential component of themagnetic field which projects beyond the target surface 34 is strongest.When the current through opposite conductors, for example steeringconductors 62 and 64, is equal or balanced (i.e. I₁=I₂), the arc spottravels along a narrow erosion corridor largely confining the erosionzone 70 beneath the apex of the magnetic field lines symmetrically aboutthe longitudinal centre of the cathode plate 32, as shown in FIG. 2a.

[0072] According to one aspect of the invention, by increasing thecurrent in one steering conductor relative to the current in thesteering conductor on the opposite side of the cathode plate 32, themagnetic field becomes unbalanced and the magnetic field lines on theside of the cathode 32 with the weaker magnetic field shift toward theside of the cathode 32 with the stronger magnetic field. In thepreferred embodiment each linear conductor 62, 64, 66, 68 is thuselectrically independent and can be controlled in isolation.

[0073] For example, in FIG. 2b the current in steering conductor 62 hasbeen increased relative to the current in steering conductor 64, so thatI₁<I₂. The resulting unbalancing of the strength of the magnetic fieldsgenerated thereby distorts the magnetic field generated by the conductor64 and shifts its magnetic field lines toward the conductor 62. Thepoint of the magnetic field generated by conductor 64 where thetangential component of the transverse magnetic field is strongest hasthus shifted away from the side 32 a and toward the centre of thecathode 32, and arc spots accordingly trace a path closer to the centreof the cathode 32. By unbalancing the current in conductors 62, 64 sothat conductor 64 generates the stronger magnetic field and I₁>I₂, thepath of the arc spot shifts away from the side 32 b and toward thecentre of the cathode, as shown in FIG. 2c.

[0074] The degree of unbalancing, i.e. the current differential betweenconductors 62 and 64, determines the extent of the magnetic field shift.By unbalancing the conductors 62, 64 at selected current levels and inproperly timed intervals coinciding with the motion of the arc spot, aplurality of arc spot paths are created. This substantially increasesutilization efficiency of the target surface.

[0075] A similar effect is achieved along the short sides 32 c, 32 d ofthe cathode 32 by unbalancing the current through the conductors 66, 68.The path of the arc spot will shift toward the centre of the cathode 32along the side with the weaker magnetic field. However, it will beappreciated that if the cathode plate 32 is narrow enough that themagnetic fields generated along the long sides 32 a, 32 b by conductors62, 64 are relatively close together, the conductors 66, 68 along theshort sides 32 c, 32 d may become unnecessary; the arc spot willnaturally migrate back and forth between the long magnetic fields, or asthe arc spot reaches the end of its path along one long side 32 a or 32b the magnetic field can be selectively decreased or momentarilydeactivated along that side and the arc spot will move to the other side32 b or 32 a where the magnetic field is stronger.

[0076] The closing conductors 62 a, 64 a, 66 a, 68 a, which are parallelto the target surface 34 and respectively complete the circuit for eachsteering conductor 62, 64, 66, 68, are maintained well away from thecathode plate 32 and the housing 38. This ensures that the magneticfields generated by the closing conductors 62 b, 64 b, 66 b, 68 b or 72a, 72 b do not influence arc spot formation or plasma flow patterns.

[0077] In operation, when an arc is created by applying a currentbetween the anode and the cathode plate, an arc spot generated on thetarget surface 34 settles in an erosion corridor 70 defined within thesteering magnetic fields generated by the steering conductors 62, 64,66, 68. The arc spot follows a retrograde motion along the erosion zone70. The magnetic field is periodically unbalanced by a control switch(not shown), which intermittently increases the current throughconductor 62 to increase the strength of the magnetic field generatedthereby and shift the arc spot path away from the side 32 a, andalternately increases the current through conductor 64 to increase thestrength of the magnetic field generated thereby and shift the arc spotpath away from the side 34 a. This effectively widens the erosion zone70 to increase the utilization efficiency of the target surface,improving the quality of the coating and the durability of the cathode32.

[0078] In a variation of this embodiment, illustrated in FIG. 3, aplurality of steering conductors 62 b, 62 c, 62 d and 64 b, 64 c, 64 dare provided respectively along the long sides of the cathode plate 32.In this variation the steering conductors 62 b, 62 c, 62 d and 64 b, 64c, 64 d are activated or modulated alternatively so that the erosioncorridor, being located generally above the currently active steeringconductor 62 b, 62 c or 62 d on one side and 64 b, 64 c or 64 d on theother side, can be shifted in a widthwise direction over the cathodeplate 32 to increase the breadth of the erosion zone 70.

[0079] In the embodiment of FIG. 3 as many steering conductors may beprovided as the size of the cathode plate 32 will practically allow. Onesteering conductor 62 b, 62 c or 62 d and 64 b, 64 c or 64 d should beactive on each side of the cathode plate 32 at any particular time, inorder to avoid creating a stagnation zone in which the cathode spot maybecome trapped. However, where the conductors on each side of thecathode 32 are close together, simultaneously exciting more than oneconductor on each side of the cathode 32 can allow for a more elaborateerosion pattern which, properly controlled, can increase the utilizationefficiency of the target surface 34 even further.

[0080] In the operation of this embodiment, when an arc is created byapplying a current between the anode and the cathode plate, an arc spotgenerated on the target surface 34 settles in an erosion corridor 70defined within the steering magnetic fields generated by the activesteering conductors, for example 62 b and 64 b. The magnetic field isperiodically shifted by a control switch (not shown), which switches thecurrent between the conductors 62 b, 62 c and 62 d on the long side 32 aand between the conductors 64 b, 64 c and 64 d on the long side 32 b, tothereby and shift the arc spot path to the vicinity of the activesteering conductor. This widens the erosion zone 70 to increase theutilization efficiency of the target surface, improving the quality ofthe coating and the durability of the cathode 32.

[0081] It will be appreciated that in each of these embodiments theactive steering conductor does not need to be deactivated completelywhen another steering conductor is activated, or fully energized whenactivated, in order to achieve the desired erosion pattern in theerosion zone 70. The current can be modulated differentially as betweenthe various steering conductors to generate the same result.

[0082] FIGS. 4 to 6 illustrate a further embodiment of the inventionproviding arc spot shielding. An arc coating apparatus 30 is providedwith a rectangular cathode plate 32 comprising a target evaporationsurface 34 and a supporting plate 36 mounted to a cathode holder 42,within a coating chamber defined by the target surface 34 and a housing38. In the preferred embodiment the target surface 34, which may becomposed of any suitable metallic or a non-metallic coating material,has long sides 32 a, 32 b and short sides 32 c, 32 d and is electricallyinsulated from the housing 38 by dielectric spacers 39 isolating thecathode holder 42 from the supporting plate 36 and spaced from thehousing 38 by a gap 40. The target surface 34 may be formed fromdifferent materials, for example titanium and aluminum or titanium andchromium, integrated in a mosaic fashion along the erosion zone 70 toproduce a composite metallic plasma for applying coatings such as TiAlN,TiCrN or the like.

[0083] The cathode plate 32 is spaced from the cathode holder 42 tocreate a coolant chamber 44 for circulating a coolant such as water, andis connected to the negative pole of an arc current source (not shown).A conventional high voltage pulse igniter 48 is mounted through adielectric sleeve traversing the wall of the housing 38.

[0084] Suspended from the housing 38 by a mounting assembly 51 is aplurality of linear anodes 50, spaced from the cathode plate 32 andmounted to respective anode holders 52 which may be provided with acoolant channel 53 for circulation of a coolant such as water. Theanodes 50 are connected to the positive pole of the arc current sources46. In the preferred embodiment the anodes 50 each comprise a series ofbaffles or “fins” 50 a which may be disposed generally orthogonally inrelation to an anode body 50 b, to increase the effective anodic surfacearea. The fins 50 a and anode body 50 b are each preferably oriented ina direction parallel to the direction of the plasma flow, i.e. parallelto the direction of any focusing magnetic fields in the vicinity of theanode 50 as described below, to reduce the opportunity for vapourdeposition on the anodic surfaces and thus reduce diffusion losses.

[0085] Arc spot formation is confined by steering magnetic fieldsproduced by a steering magnetic field source 60 comprising linearconductors 62 and 64 respectively disposed along the long sides 32 a, 32b of the cathode plate 32 and linear conductors 66 and 68 respectivelydisposed along the short sides 32 c, 32 d of the cathode plate 32. Inthis embodiment the conductors 66, 68 are disposed behind the cathodeplate 32 as in the previous embodiments, but the conductors 62, 64 aredisposed in front of the cathode plate 32. The conductors 62, 64 arestill disposed in the vicinity of the target surface 34 so that themagnetic fields generated thereby influence arc spot formation andmotion, and the operation of the steering system 60 in this embodimentis substantially as described in respect of the embodiment of FIG. 2.

[0086] However, in the embodiment of FIGS. 4 to 6 the steering magneticfields do not confine arc spots, as in the embodiment of FIG. 2, becausethe magnetic field lines are not arch-shaped and intersect the targetsurface 34 on only one side, as seen by the magnetic field lines shownin FIG. 5. Thus, because of the acute angle principle arc spots areguided toward the central region of the cathode plate 32, away from theacute angle formed where the magnetic field lines intersect the targetsurface 34. Arc spots therefore have a broader range of motion availablein this embodiment. Moreover, in the embodiments in which the steeringconductors are located behind the cathode plate 32, in which the portionof the steering magnetic fields projecting above the target surface 34is closed (i.e. intersects the target surface 34 along both sides), themagnetic fields confine not only the arc spot but also the plasmagenerated as the target surface 34 evaporates. As shown in FIG. 5, bydisposing the conductors 62, 64 in front of the target surface 34 thecathodic evaporate has an open path to the substrate holder 6.

[0087] Arc spots are thus guided toward the central region of thecathode plate 32, from both long sides 32 a, 32 b. To avoid creating astagnation zone in the central region of the cathode plate 32, aconductive shield 54 maintained at floating potential is mounted to eachanode holder 52, insulated therefrom and spaced from the targetevaporation surface 34, which precludes any cathode spot activity in thecentral region of the cathode plate 12. Preferably the shield 54 isspaced from the target surface 34 between 2 mm and 6 mm; less than about2 mm is likely to cause the arc to short circuit through the shield 54and more than about 6 mm allows the arc spot to creep under the edges ofthe shield 54. The shield 54 thus prevents evaporation of the cathode 32in the shadow of the anode 50, confining arc spot formation to anerosion zone 70 surrounding the shadow of the anode 50. This protectsthe anode 50 from deposition of cathodic evaporate and provides a betterdistribution of coating material over the substrates (not shown) mountedon the substrate holder 6.

[0088] One or more floating shields 54 may be positioned over anyselected portion(s) of the target evaporation surface 34, to prevent arcspots from moving into the shielded region. In the embodimentillustrated the shield 54, positioned immediately above the targetsurface 34 in the vicinity of the anode 50, prevents arc spots fromforming in or moving into the area of the target surface 34 surroundingthe shield 54. This is advantageous in embodiments in which the steeringconductors are disposed in front of the cathode plate 32. However, afloating shield 54 can be used to keep arc spots away from any desiredregion of the cathode plate 32. For example, the floating shield 54allows the target evaporation surface of the cathode plate to beconstructed of more than one material; in this case an expensive coatingmaterial such as tungsten or platinum can be omitted from the regionbeneath the shield 54, and since arc spots will not form or move in thatregion there is no possibility that the coating will be contaminated.

[0089] In operation, a current is applied between the anode 50 and thecathode plate 32 and a high pulse voltage applied to igniter 48initiates a vacuum arc on the target evaporation surface 34 of thecathode plate 32. The arc spot settles in an erosion corridor 70 definedbetween the steering magnetic fields generated by the conductors 62, 64and the shielded region of the target surface 34 behind the conductiveshields 54. The arc spot follows a retrograde motion along one long side32 a or 32 b of the target surface 34, and moves to the other long side32 b or 32 a traveling beneath the apex of the magnetic field generatedby the steering conductor 66 or 68 disposed behind the cathode plate 32.As the target surface 34 evaporates the plasma is guided between themagnetic fields generated by the conductors 62, 64 and flows toward thesubstrate holder 6, as shown by the arrows in FIG. 5.

[0090] Because the preferred embodiments of the invention employ amagnetic steering system, it is possible to use a plasma focusing systemto guide the cathodic evaporate toward the substrate holder 6. Amagnetic field forms a barrier which is largely opaque to plasma. Thus,focusing magnetic fields can be generated about the housing 38 toconfine the plasma to a plasma flow region between magnetic fields, andpositioning the substrate holder 6 in the plasma flow region toincreases the concentration of plasma about the substrates and improvesthe quality of the coating.

[0091] In the embodiment illustrated in FIGS. 4 to 6 the conductors 62,64, being disposed in front of the target surface 34 of the cathodeplate 32, can also serve as focusing conductors in a plasma focusingsystem 80. A plasma flow path is defined between the magnetic fieldsgenerated by the conductors 62, 64, as shown by the magnetic field linesin FIG. 5, such that plasma is guided along a central region of thehousing 38 to the substrate holder 6. In this embodiment it isadvantageous to provide the short side steering conductors 66, 68 withseparate power sources, which allows for the strength of theirrespective magnetic fields to be varied independently, to compensate forany distortion in the steering magnetic fields caused by the long sidesteering conductors 62, 64 and thus properly position the arc spot inthe erosion corridor 70.

[0092] In the embodiment illustrated in FIG. 6b, a plurality of pairs ofsteering conductors 66, 68 are provided behind a single cathode plate32, corresponding to the plurality of anodes 50. In this embodiment aseparate erosion corridor can be provided for each anode 50,respectively associated with each pair of steering conductors 66, 68parallel to the short sides of the cathode plate 32, because the twointermediate steering conductors 66, 68 prevent arc spots from migratingpast the center of the cathode plate 32.

[0093] To focus the plasma flow, additional plasma focusing conductorsmay be provided in series to elongate the plasma flow path. For example,FIGS. 7a to 7 d illustrate embodiments of the invention having aplurality of linear anodes 50 in which groups of plasma focusingconductors 82, 84 and 92, 94 are disposed on opposite sides of thehousing 38 and, within each group, progressively further from thecathode 32. This creates a plasma confining zone between the magneticfields generated on opposite sides of the housing 38, thus defining aplasma flow path between the target surface 34 and the substrate holder6.

[0094] The focusing conductors 82, 84 and 92, 94 are preferably disposedtoo far from the cathode plate 32 to influence arc spot formation ormotion. Preferably also the focusing conductors in each group 82, 84 or92, 94 are disposed in closely spaced relation so that their respectivemagnetic fields overlap to create a continuous magnetic path confiningthe plasma flow and magnetically isolating the wall of the housing 38from the plasma flow; otherwise plasma may be trapped against the wallsof the housing 38. As in the case of the steering conductors, theclosing conductors 82 a, 84 a of the focusing conductors 82, 84 and theclosing conductors 92 a, 94 a of the focusing conductors 92, 94 aremaintained well away from the housing 38 and the cathode plate 32 toeliminate any canceling effect of the magnetic fields generated therebyin the region of the housing 38 (plasma duct). In this embodiment it maybe advantageous to provide the short side steering conductors 66, 68with separate power sources, to compensate for any distortion in thesteering magnetic fields caused by the focusing conductors 92, 94.

[0095] In the operation of this embodiment, as the target surface 34evaporates the plasma is concentrated between the focusing magneticfields generated by focusing conductors 82, 84 and 92, 94. The plasmathereby flows toward the substrate holder 6 without contacting thehousing 38.

[0096] The focusing conductors 82, 84 and 92, 94 are preferablyindependently powered, so that the intensity of the magnetic fieldgenerated by each conductor 82, 84, 92, 94 can be varied independentlyof the others. Closed loop focusing conductors can be disposed aroundthe housing 38, however in the preferred embodiments illustrated inFIGS. 7a, 7 b pairs of independent focusing conductors 82 and 92, and 84and 94, respectively, are disposed on opposite sides of the housing 38parallel to the long sides 32 a, 32 b of the cathode 32. The closingconductors 82 a, 84 a, 92 a and 94 a are maintained well away from thehousing 38 and the cathode plate 32.

[0097] In a further embodiment illustrated in FIG. 8 the opposedfocusing conductors 82, 92 and 84, 94 are formed from the same closedloop conductor with the focusing conductors 82, 92, 84 and 94 disposedparallel to the long sides 32 a, 32 b of the cathode 32 with closingconductors 82 a, 92 a, 84 a and 94 a disposed parallel to the shortsides 32 c, 32 d of the cathode 32.

[0098] By connecting focusing conductors 82, 84 and 92, 94 independentlyto the power supply it is also possible to “raster” the plasma flow byvarying the current through opposed focusing conductors 82, 92 and/or84, 94. This helps to distribute the plasma more uniformly about theplasma duct and to create a more homogeneous plasma mixture. Within thecoating chamber the focusing conductors 82, 84 and 92, 94 can beindependently activated to deflect plasma toward the substrate holder 6.

[0099]FIG. 8 illustrates a mode of reducing the magnetic influence ofthe closing conductors 82 a, 92 a using neutralizing conductors 140comprising closed-loop coils disposed alongside closing conductors 82 a,92 a, but in an opposite orientation. When activated the neutralizingconductors 140 eliminate the influence of closing conductors 82 a, 92 aon the plasma flow. The neutralizing conductors 140 can also raster theplasma flow slightly in the vicinity of the walls of housing 38 parallelto the short sides 32 c, 32 d of the target 32.

[0100] In all embodiments the closing conductors 82 a, 84 a, 92 a and 94a are maintained well away from the housing 38 and the cathode plate 32to eliminate any canceling effect of the magnetic fields generatedthereby in the region of the housing 38 (especially the plasma ductregion of the housing 38).

[0101] The plasma focusing system of the invention can also be used as aplasma deflecting system 100, allowing the substrate holder 6 to bedisposed remote from the working axis of the cathode plate 32,designated 33 in FIG. 9, to eliminate from the plasma the neutralcomponent (macroparticles, clusters and neutral atoms) which areunaffected by the focusing magnetic field and further improve thequality of the coating. As shown in FIG. 9, by arranging deflectingconductors 86, 87, 88 and 96, 97, 98 along a curvate housing 38 in aprogressively asymmetrical pattern relative to the working axis 33 ofthe cathode plate 32, the plasma is deflected toward the substrateholder 6 while the inertia of the plasma causes the neutral component toseparate from the plasma in the deflection region.

[0102] The conductors 86, 87, 88 and 96, 97, 98 thereby create a chainof deflecting conductors to form a deflecting electromagnetic system. Asin the previous embodiments, closing conductors 86 a, 87 a, 88 a and 96a, 97 a, 98 a are maintained well away from the housing 38 (especiallythe plasma duct region) and the cathode plate 32. The closing conductors86 a, 87 a, 88 a and 96 a, 97 a, 98 a may be disposed on the same sideof the housing 38 as the deflecting conductors 86, 87, 88 and 96, 97, 98of the deflecting system, for example by disposing the closingconductors 86 a, 87 a, 88 a and 96 a, 97 a, 98 a well above or below thelevel of the housing 38. Alternatively the closing conductors 86 a, 87a, 88 a and 96 a, 97 a, 98 a may be disposed on the opposite side of thehousing 38 but remote therefrom, in which case it is preferable that thedistance S between the closing conductors and focusing conductorsarranged along opposite sides of the housing (for example focusingconductors 86, 87, 88 and closing conductors 96 a, 97 a, 98 a) rangesfrom 1.5H to 3H where H is the width (transverse) of the housing 38.

[0103] In the operation of this embodiment, as the target surface 34evaporates the plasma is concentrated between the magnetic fieldsgenerated by the conductors 62, 64 and flows into the deflection regiondefined between the magnetic fields generated by deflecting conductors86, 87, 88 and 96, 97, 98. The plasma is thereby deflected along a flowpath coinciding with the asymmetrical pattern of the deflectingconductors 86, 87, 88 and 96, 97, 98 and flows toward the substrateholder 6 without contacting the housing 38. The plasma remains confinedbetween magnetic fields and is thereby deflected away from the workingaxis 33 of the cathode plate 32. The neutral component continues in agenerally straight direction and settles on an interior wall of thehousing 38 in the vicinity of the working axis 33 of the cathode plate32, while the plasma continues along the plasma duct into the coatingchamber to the substrate holder 6.

[0104]FIG. 10 illustrates a preferred embodiment of an arc coatingapparatus according to the invention, providing a pair of cathode plates32 disposed in a cathode chamber at opposite ends of the housing 38, incommunication with the substrate holder 6 through a parallelipedalplasma duct 31. Internal linear anodes 50 configured as described aboveare suspended above each target surface 34, separated therefrom by ashield 54. Anodes 50 are defined herein as “internal” because they aredisposed within the plasma duct, which is defined between the cathodeplates 32 and the substrate holder 6.

[0105] A further internal anode, deflecting electrode 120 comprising alinear plate 122 having baffles 124, is disposed along the plasma duct31 at the approximate center between the two cathode plates 32. Thebaffles increase the anodic surface area, effectively functioning as achain of internal anodes, which provides better stabilization andsteering of arc spots. They also serve to trap macroparticles emittedfrom the evaporation surface 34. As in the previous embodiment, thebaffles 124 are oriented as much as possible parallel to the directionof the magnetic field to reduce diffusion losses. This “dividing” anode120 also serves to repel ions and thus deflect the plasma streams towardthe substrate holder 6.

[0106] In this embodiment focusing conductors 82, 84, 92 and 94 aredisposed parallel to the long sides 32 a, 32 b of the cathode platesboth about the regions in front of the cathode plates 32 and about theexit of the plasma duct 31 in the coating chamber. In between the setsof focusing conductors 82, 92 and 84, 94, deflecting conductors 86, 96are disposed about the portion of the housing 38 where the plasma duct31 turns toward the axis of the substrate holder 6, i.e. adjacent to aportion of the housing 38 containing the cathode plates 12, creatingopposed magnetic cusps directed perpendicular to the axis of the cathodechamber, to thus deflect plasma toward the substrate holder 6. In theembodiment shown the closing conductors 82 a, 84 a, 86 a, 92 a, 94 a and96 a must be disposed remote from the plasma duct 31 in order to ensurethat the cathode plates 32 are disposed only within the magnetic cuspsgenerated by the focusing and deflecting conductors 82, 84, 92, 94 and86, 96, so that cathodic evaporate is drawn into the plasma duct 31 andnot toward the back wall of the housing 38. Alternatively, as in theembodiment of FIG. 9 the closing conductors 82 a, 84 a, 86 a and 92 a,94 a, 96 a may be disposed on the opposite side of the housing 38 butremote therefrom.

[0107] The embodiment of FIG. 10 also provides one or more externalanodes 130 surrounding the substrate holder 6. Anodes 130 are definedherein as “external” because they are disposed outside of the plasmaduct 31. Thus, the external anodes 130 do not deflect the plasma, butinstead repel ions to prevent diffusion losses on the walls of thehousing 38 and prolong ionization of the coating material to improvecoating efficiency. Such external anodes 130 can also be provided aboutany desired portion of the housing 38.

[0108] Further, since the housing 38 is insulated from the cathodeplates 32 by dielectric spacers 39, the housing 38 may be left atfloating potential as shown in the Figures. Alternatively, providing afloating potential screen or shielding (not shown) between the cathode32 and the housing 38 to prevent the arc from moving into a gap betweenthe cathode 32 and the housing, will effectively turning the housing 38into an external or surrounding anode.

[0109] The internal anodes 32, 120 and external anode 130 are preferablyelectrically isolated and thus each is provided with an independentpower supply, which allows for better control over their independentfunctions.

[0110] It is also possible to differentially activate the focusingconductors 82, 84 and 92, 94 to trap the metal vapour component of theplasma within the plasma duct while allowing the electron current toflow freely through the coating chamber to the auxiliary anodes 130surrounding the substrate holder 6. This mode of operation is a “plasmaimmersed” mode, which provides a high degree of ionization andactivation of the gaseous plasma environment in the coating chamberwithout deposition of metal cathodic arc plasma coatings. The plasmaimmersed mode supports several different types of plasma processes, suchas fast ion cleaning, ion nitriding, ion implantation, and arcplasma-assisted low pressure CVD coating processes. For example, thefirst stage of a particular coating process may require ion cleaning.The cathodic arc sources 34 may be used as a powerful electron emitters,to extract electron current from the cathode to the external anode 130surrounding the substrate holder 6, providing a plasma immersedenvironment for fast ion cleaning. Argon, nitrogen, methane etc. may beinjected as a plasma-created gas in conjunction with an RF generatorproviding a self bias potential at the substrate holder for effectiveion bombardment, as illustrated by the examples.

[0111]FIGS. 7c and 7 d illustrate a further embodiment of the invention,similar to the embodiment of FIGS. 7a and 7 b but providing multiplerectangular cathode targets incorporated in one rectangular cathodic arcsource unit. Housing 38 contains two rectangular cathode assembliesconsisting of target plates 34 attached to water cooled target holder 32and vacuum arc ignitors 170. Each cathode target assembly is surroundingby an insulated shield 140, which prevents cathodic arc spots frommoving toward side surface of the cathode assembly. Central anode 50 canbe optionally installed in front of the cathode target plate 32. Theinsulated shield 54 can be installed in a central area of the targetplate 32, to prevent cathodic arc spots from moving toward central areaof the target where the steering magnetic field component that istangential to the plate surface 34 is not sufficient to confine arcspots within the erosion corridor 200. Two pairs of focusing magneticcoils 84 and 62 are using to steer cathodic arc spots along long sidesof the targets 32, while simultaneously focusing the plasma flow towardthe substrate holder 6 installed in the main vacuum chamber. Anotherpair of magnetic coils 66, 68 is disposed on a back side of each cathodeassembly. The linear conductors 66, 68 are parallel to the short sides32 c, 32 d of the cathode targets 32, providing steering of cathodic arcspots along short sides of the target surface 34. Conductors 66, 68 mustbe installed with opposite polarities, providing steering of cathodicarc spots in the same direction as adjacent focusing conductors 62, 84steering cathodic arc spots along the erosion corridor 200. Surroundinganodes 150 can be optionally sectioned or partitioned, providingindependent anodic current circuits for cathodic arc spots located bothnear the short sides 32 c or 32 d of the target plate 32 (anodic pair151-151 a in the embodiment shown in FIG. 7d) and long sides 32 a or 32b of the cathode target 32 (anodic pair 152-152 a in the embodimentshown in FIG. 7d). This also allows for the detection of cathodic arcspots stagnating near the short sides or long sides of the targetsurface 34. As soon cathodic arc spots are located near either short orlong side of the target surface 34 for time longer thant_(s)˜l_(s)/v_(s), (where l_(s) is a length of a short or long side ofthe cathode target plate 34, v_(s) is a velocity of a movement ofcathodic arc spots under influence of steering magnetic field), the arccurrent can be turned off to eliminate the arc spots, followed byre-ignition of the arc by igniters 170. Sectioning or partitioning theanodes, including both surrounding 151, 152 and central 50, allows forthe optimal distribution anodic arc current to provide maximumreliability of steering of arc spots inside of erosion corridor 200.

[0112] Alternatively, instead of a shield (either a shield 140 aroundthe cathode plate 32 or a shield 54 covering the stagnation zone infront of the evaporation surface 34), the cathode plate 32 can besurrounded by a material that has a very low cathodic arc spotsustainability, or this material can be inserted in the area of thecathode plate 32 where arc spots are stagnating. For example tungsten,molybdenum, boron nitride-based ceramics etc., can be used to preventarc spots from moving in undesirable areas of the evaporation surface34.

[0113] FIGS. 11 to 13 illustrate a further embodiment of the inventionproviding local correctional magnets 200 and 210 for guiding the arcspot between one long side 32 a of the cathode plate 32 and the otherlong side 32 b, and providing a different anode arrangement.

[0114] Short side correctional magnets 200 preferably each comprise atleast one magnetic coil 202 surrounding an electromagnetic core 204, andare respectively disposed along the short sides 32 c, 32 d of thecathode plate 32. The core 202 concentrates the magnetic field generatedby the coil 202, so that when the coil 202 is activated the arc spot isconstrained to move along the arc-shaped magnetic field lines whichextend over the short side 32 c or 32 d of the cathode plate 32.

[0115] In this embodiment long side correctional magnets 210 are alsoprovided along both long sides 32 a, 32 b of the cathode plate 32, nearthe short sides 32 c, 32 d, to similarly constrain the motion of the arcspot as the arc spot nears the short sides 32 c, 32 d. Long sidecorrectional magnets 210 similarly preferably each comprise at least onemagnetic coil 212 surrounding an electromagnetic core 214 whichconcentrates the magnetic field generated by the coil 212, so that whenthe coil 212 is activated the arc spot is constrained to move across themagnetic field lines in a direction transversal to the arc-shapedmagnetic field lines which extend over the ends of the long side 32 a or32 b.

[0116] The directions of the magnetic field lines generated by thecorrectional magnets 200, 210 must correspond to the motion of the arcspot along the long sides 32 a, 32 b as determined by the steeringconductors 66, 68 (shown in FIG. 11). The correctional magnets 200, 210act on the arc spot only as it nears and traverses the short sides 32 c,32 d of the cathode plate 32, to maintain an uninterrupted steeringpattern about the cathode plate 32. The strength of the magnetic fieldsgenerated by the correctional magnets 200, 210 can be varied by varyingthe current through the coils 202, 212 or by providing additional coils(not shown) surrounding the cores 204, 214 which can be selectivelyactivated to superimpose an additional magnetic field onto the core 204or 214.

[0117] In this embodiment a linear internal anode 220 comprises a seriesof anode blocks 222 and 230. Interior anode blocks 222 provide an anodeplate 224 and baffles 226 disposed generally orthogonally in relation toan anode plate 224. As in the previous embodiments the anode plate 224and baffles 226 are each oriented in a direction parallel to thedirection of the plasma flow. The anode 220 further includes end anodeblocks 230, preferably comprising solid water-cooled blocks, which serveto isolate the interior regions of the anode 220 from cathodic evaporateeroded from the short sides 32 c, 32 d of the cathode plate 32. The useof separate “blocks” helps to better distribute the arc current andreduces reliance upon a single anode body.

[0118] The anode blocks 222, 230 are preferably independently controlledby separate power supplies 227 disposed through water-cooled anode pipes229, mounted to and insulated from the housing (not shown) by insulatingspacers 228. The strength of the current through an anode block 222 or230 determines the absence or presence of an arc spot, and thus suitablesoftware can be employed to raster or scan through the blocks 222, 230within the anode 220 in concert with the motion of the arc spot aboutthe erosion zone 70. This arrangement helps to reduce the intervalduring which the arc spot is passing from one long side of the cathode32 to the other. Moreover, if the arc spot stagnates at any point alongthe erosion corridor 70, the power supply to an adjacent anode block 222or 230 can be deactivated or reduced, and/or the power supply to a moreremote anode block 222 or 230 can be activated or increased, to keep thearc spot in motion.

[0119] The linear focusing conductors 82 and 84 shown in FIG. 12(partially concealed by the flange 250) are respectively disposed infront of the evaporation surface along the long sides 32 a, 32 b of thecathode plate 32. Focusing conductors 82, 84 produce a tangentialmagnetic field which steers (drags) the arc spot along long sides 32 a,32 b of the cathode plate 32. Because they are disposed in front of theevaporation surface 34, the focusing conductors 82, 84 create a magneticcusp directed toward the coating chamber 38 (similar to that indicatedby the arrows FIG. 5). The cusp configuration tends to guide arc spotstoward the center of the cathode 32, which renders the shield 54particularly advantageous in this embodiment as it prevents the arc spotfrom moving into the shadow of the anode 220, where the magnetic fieldlines are generally perpendicular to the evaporation surface 34 andwithout the shield 54 would create a stagnation zone in the centerregion of the cathode 32.

[0120] In this embodiment the closing conductors 82 a, 84 a are disposedbehind the evaporation surface 34 along the long sides 32 a, 32 b of thecathode plate 32 produce a magnetic field having an arch shape over theevaporation surface 34, which balance the acute cusp-shaped magneticfield lines produced by the focusing conductors 82, 84 and act inconjunction with the steering conductors 66, 68 respectively disposedalong the short sides 32 d, 32 c of the cathode plate 32, along with thecorrectional magnets 200, 210 which also guide arc spots along the shortsides 32 d, 32 c of the cathode plate 32, to guide arc spots in the samedirection around the erosion zone 70.

[0121] Thus, the conductive shield 54 spaced from the target evaporationsurface 34, together with a border shield 55 disposed about theperiphery of the cathode plate 32, precludes any cathode spot activityoutside of the desired erosion zone 70. In the embodiment shown aninternal shield 57 is provided beneath the shield 54, which also servesto prevent cathode spot activity in the shadow of the anode 220.

[0122] In the embodiment of FIGS. 11 to 13 a surrounding anode 240 isprovided around the evaporation surface 34, generally orthogonallythereto. The surrounding anode 240, which is disposed in front of theevaporation surface 34, becomes a plasma-immersed anode which improvescurrent exposure to the plasma flow and provides a more stable arccurrent surrounding the primary anode 220. The apparatus of theinvention will operate with either the “internal” anode 220 or thesurrounding anode 240; however, operation of the apparatus is improvedby employing both anodes 220, 240 simultaneously.

EXAMPLE 1

[0123] Deposition of a diamond-like coating (DLC) on set of knives suchas scalpels, razors, knives for cutting papers using two rectangular arcsources mounted in the dual rectangular plasma guide chamber of FIG. 10with deposition zone 500 mm height×300 mm width. The array of knives wasinstalled on a rotating substrate platform facing the filtered arcsource over the entire area of the deposition zone, with uniformrotation speed between about 10 to 20 rpm. A graphite rectangular plateevaporation target was attached to the cathode plate assembly. Thecurrent in the vertical steering conductors was set to 2000 amps, andthe current in the horizontal steering conductors was set to 1300 amps.The arc current between the cathode and the primary (internal) anodeplate was set to 300 amps. After igniting the arc with an impulse highvoltage igniter, the arc spot began moving along an erosion corridorwith an average speed ranging from 20 to 30 cm/s. About three to fivecathodic arc spots subsisted simultaneously on the target surface. Thecurrent in the deflecting coils was set to 1500 amps each.

[0124] The first stage of the process involved ion cleaning. At thisstage the cathodic arc sources were used as a powerful electronemitters. The deflecting conductors were turned off and electron currentwas extracted from the cathode to the auxiliary (external) anodesurrounding the substrate platform, providing a plasma immersedenvironment for fast ion cleaning. Argon was injected as aplasma-created gas with pressure of about 4×10⁻² Pa and an RF generatorprovided a 400 volt self bias potential at the substrate platform foreffective ion bombardment.

[0125] During the deposition stage the pressure in the vacuum chamberwas set to 10⁻³ Pa. The RF generator having a 13.56 MHz frequencyprovided a self bias potential ranging from 40 V to 60 V duringdeposition. The deflecting coils were turned off during depositionperiodically with a duty cycle of 20 s on/5 s off to prevent overheatingof the coating. The time of deposition was 20 minutes. The thickness ofthe coating, as measured by micro cross section, ranged from 0.3 to 0.35mkm which corresponds to a deposition rate of about 1 mkm/hr with auniformity of +/−10%.

EXAMPLE 2

[0126] Deposition of graphite coating on molybdenum glass for using as asubstrate for flat panel display using rectangular molybdenum glassplates with dimensions 400 mm height×200 mm width×3 mm thick installedvertically on the rotating substrate platform. Each glass plate wasattached to a metal plate-holder and a self bias of about 150 V wasapplied to the substrate platform using an RF generator with a 13.56 MHzfrequency. The dual filtered cathodic arc source of FIG. 10 was providedwith one aluminum target evaporation surface and one graphite targetevaporation surface. The pressure during coating deposition wasmaintained at about 10⁻³ Pa. The temperature during deposition of thegraphite coating was about 400° C., provided by an array of radiativeelectrical heaters.

[0127] In the first stage the arc was ignited on the aluminum target,providing an aluminum sublayer with thickness about 50 nm. In the secondstage a graphite coating with thickness about 150 nm was deposited overthe aluminum sublayer during a coating interval of 30 minutes.

EXAMPLE 3

[0128] Deposition of TiAlN coatings on an array of hobs and end mills.The array of hobs and end mills was installed on substrate platformfacing the filtered arc source exit over the entire area of thedeposition zone, the substrate platform having a double (satellite)rotation with platform rotation speed 12 rpm. The dual rectangularfiltered arc source of FIG. 10 was provided with an aluminum targetevaporation surface mounted to one cathode and a titanium targetevaporation surface mounted to the second cathode, for deposition of theTiAlN coating. The current for the titanium target was set at about 150amps while current for the aluminum target was set at about 60 amps.

[0129] In the first stage the current of the auxiliary (external) anodewas set at about 70 amps, providing a high density gaseous plasmaimmersed environment during both fast ion cleaning and coatingdeposition. The self bias potential of substrate platform provided by aRF 13.56 MHz generator was maintained at about 400 volts during ioncleaning in argon, and at about 40 volts during deposition of TiAlNcoating in nitrogen. The time for ion cleaning was 5 minutes, and fordeposition was about 2 hours. The argon pressure during ion cleaning wasset at 6×10⁻² Pa of argon, and for the deposition stage it was set at2×10⁻² Pa of nitrogen. The deposition rate for TiAlN coating for doublerotated hobs and end mills was found to be about 1-1.5 μm/hr.

EXAMPLE 4

[0130] Deposition of multi-layer coatings on dies and molds. An array offorging dies and extrusion molds was installed on the substrate platformwith uniform rotation speed 20 rpm facing the filtered arc source exitin the dual rectangular filtered arc source of FIG. 10, for thedeposition of Ti/TiN multi-layer coating with thickness ratio 0.05 μm ofTi and 0.3 μm of TiN. Before deposition of the coatings fast ioncleaning and arc plasma immersed ion nitriding was performed to providegradually increased hardness of near surface layer in a transition zonebetween bulk material of coating parts and the coating layer. Thethickness of nitriding layer was about 40 μm, provided by an auxiliaryarc discharge with the current of auxiliary (external) anode set atabout 90 amps and a pressure of nitrogen set at about 6×10⁻² Pa. Thenumber of coating layers was 11 with total thickness about 3.5 μm. Thecurrent of the auxiliary anode during the deposition stage was set atabout 120 amps, providing maximum total current at both titanium targetsof about 500 amps. The DC bias during the ion cleaning/ion nitridingstage was set at about 200 volts, and during the deposition stage thecurrent was reduced to 40 volts. The temperature of substrates wasmaintained at about 400° C. during all stages of the vacuum plasmatreatment cycle.

[0131] Preferred embodiments of the invention having been thus describedby way of example, modifications and adaptations will be apparent tothose skilled in the art. The invention includes all such modificationsand adaptations as fall within the scope of the appended claims.

I claim:
 1. A vacuum arc coating apparatus comprising at least onerectangular cathode plate having opposed long sides connected to anegative pole of an arc current source, the at least one cathode platehaving an evaporation surface, a coating chamber defined by theevaporation surface and a housing, a substrate holder within the coatingchamber, a plurality of anodes within the coating chamber spaced fromthe evaporation surface, connected to a positive pole of a currentsource, an arc igniter for igniting an arc between the at least onecathode and each anode and generating arc spots on the evaporationsurface, and a magnetic steering system comprising at least first andsecond steering conductors arranged along opposite sides of the at leastone cathode plate, the first steering conductor carrying a current in adirection opposite to a direction of current in the second steeringconductor, the first and second steering conductors each being disposedin the vicinity of the evaporation surface so that a magnetic fieldgenerated thereby exerts a magnetic influence on the arc spot, the firststeering conductor being electrically independent of the second steeringconductor, wherein by varying a level of current applied through thefirst steering conductor relative to the second steering conductor thearc spot shifts toward a long side of the at least one cathode plate. 2.The apparatus of claim 1 in which the first and second steeringconductors are substantially linear.
 3. The apparatus of claim 1 inwhich the first and second steering conductors are orientedsubstantially parallel to the long sides of the cathode plate.
 4. Theapparatus of claim 3 in which steering conductors are also providedalong short sides of the cathode plate.
 5. The apparatus of claim 4comprising a plurality of cathode plates, in which separate steeringconductors are provided along short sides of each cathode plate.
 6. Theapparatus of claim 5 in which the first and second steering conductorsextend along the long sides of all of the plurality of cathode plates.7. The apparatus of claim 1 in which focusing conductors are providedalong the long sides of the cathode plate.
 8. The apparatus of claim 7in which magnetic fields generated by the focusing conductors confine aflow of plasma from the cathode plate to the substrate holder.
 9. Theapparatus of claim 4 in which adjacent to one cathode plate are provideda plurality of pairs of steering conductors parallel to the short sidesof the one cathode plate and having opposite polarities, to shift arcspots toward a long side of the one cathode plate both at the ends ofthe one cathode plate and at an intermediate portion of the one cathodeplate.
 10. The apparatus of claim 1 in which each of the plurality ofanodes has an associated shield covering an area of the at least onecathode in which arc spots are likely to stagnate.
 11. A vacuum arccoating apparatus comprising at least one rectangular cathode platehaving opposed long sides and opposed short sides and connected to anegative pole of an arc current source, the at least one cathode platehaving an evaporation surface, a coating chamber defined by theevaporation surface and a housing, containing a substrate holder, atleast one anode within the coating chamber spaced from the evaporationsurface, connected to a positive pole of a current source, an arcigniter for igniting an arc between the cathode and the anode andgenerating an arc spot on the target evaporation surface, and a magneticsteering system comprising at least first and second steering conductorsrespectively arranged behind the evaporation surface along the shortsides of the at least one cathode plate, the first steering conductorcarrying a current in a direction opposite to a direction of current inthe second steering conductor, the first and second steering conductorsbeing electrically independent and being disposed in the vicinity of theevaporation surface so that a magnetic field generated thereby exerts amagnetic influence on the arc spot, wherein the magnetic fieldsgenerated by the steering conductors are oriented in the same directionin front of the evaporation surface such that a level of current throughthe first and second steering conductors can be varied independently tothereby direct arc spots in a desired direction around the evaporationsurface.
 12. The apparatus of claim 11 in which the first and secondsteering conductors are substantially linear.
 13. The apparatus of claim11 in which the first and second steering conductors are orientedsubstantially parallel to the long sides of the cathode plate.
 14. Theapparatus of claim 13 in which steering conductors are also providedalong short sides of the cathode plate.
 15. The apparatus of claim 14comprising a plurality of cathode plates, in which separate steeringconductors are provided along short sides of each cathode plate.
 16. Theapparatus of claim 15 in which the first and second steering conductorsextend along the long sides of all of the plurality of cathode plates.17. The apparatus of claim 11 in which focusing conductors are providedalong the long sides of the cathode plate.
 18. The apparatus of claim 17in which magnetic fields generated by the focusing conductors confine aflow of plasma from the cathode plate to the substrate holder.
 19. Theapparatus of claim 14 in which adjacent to one cathode plate areprovided a plurality of pairs of steering conductors parallel to theshort sides of the one cathode plate and having opposite polarities, toshift arc spots toward a long side of the one cathode plate both at theends of the one cathode plate and at an intermediate portion of the onecathode plate.
 20. The apparatus of claim 11 in which each of theplurality of anodes has an associated shield covering an area of the atleast one cathode in which arc spots are likely to stagnate.